1. Overview
The fecal suction truck is generally modified from a Class II chassis. It is mainly equipped with special facilities such as a tank, a transmission system, a vacuum pump, a vacuum pipeline system, and a fecal suction hose. The vacuum technology is used to implement suction operations, which can clean and quickly transport feces and domestic sewage in septic tanks in public toilets, residential buildings, etc. to feces storage points or sewage treatment plants. If necessary, it can also be used to transport industrial waste liquids that are not very dangerous (such as low corrosion and low toxicity). It is a special sanitation vehicle that is essential for urban sanitation departments and professional sanitation workers in enterprises and institutions. The fecal suction truck is suitable for use when the suctioned material is above 0℃.
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2. Suction process
Since the suction hose is always immersed in the manure liquid, the tank body is sealed at all places. When the vacuum pump is sucking, the air in the tank is sucked out and cannot be replenished, becoming thinner and thinner, making the pressure in the tank lower than the atmospheric pressure. Under the action of atmospheric pressure, the manure liquid enters the tank body through the suction and discharge pipe to realize the suction operation.
Discharge process: The siphon pipe mouth is close to the bottom of the tank, and the ventilation direction of the four-way valve is changed to make the vacuum pump supply air to the tank body. The pressure in the tank rises and is higher than the atmospheric pressure. Under the action of compressed air, the manure liquid is discharged from the tank body through the siphon pipe and the suction hose to complete the discharge operation.
3. Main structure and function
The main structure of the manure suction truck includes the tank body, vacuum pump, power take-off, four-way valve, water-gas separator, oil-gas separator, oil storage tank, balance arm, overflow prevention valve, etc.
3.1 Tank body
The tank body is the main body of the manure suction truck, and its top is equipped with an inlet cover, air hole, and suction and discharge hole. The inlet cover is usually sealed and opened only during maintenance. The air hole is connected to the water vapor separator through the air pipe, which is the channel for air to enter and exit the tank. The suction and discharge pipe is connected to the manure suction hose on the upper side and the siphon pipe on the lower side, which is the channel for manure liquid to enter and exit the tank. The tank body is welded with a wave-proof baffle to reduce the damage to the tank body and the frame connection parts caused by the impact and vibration of the liquid when the vehicle is driving. The rear head is equipped with an observation mirror to facilitate the observation of the load and prevent the liquid level from being too high. A valve is also installed at the lower part of the rear end of the tank body, and a lower frame is welded at the lower part of the tank body. A buffer pad is installed between the lower frame of the tank body and the frame, and the lower frame of the tank body is bolted and fastened to the frame.
3.2 Power take-off
The power of the engine drives the operation of the vacuum pump through the power take-off and the transmission shaft. The power take-off is installed on the right side of the transmission, and the upper part of the operating handle is located in the middle of the cab. The power take-off consists of an input gear, an intermediate gear, an output gear, a gear shaft, a fork shaft, a fork and an operating handle. The input gear and the output gear of the transmission are always in mesh. Before starting the vacuum pump, the transmission should be put into neutral, then the engine should be started, the clutch should be disengaged, and the power take-off switch should be turned on. At this time, the fork shaft moves forward, and the power is transmitted from the transmission output gear to the power take-off input gear, and then to the output gear through the intermediate gear, and then to the transmission shaft through the coupling, thereby driving the vacuum pump to operate.
3.3 Vacuum Pump
The feces suction truck adopts the XD-70 vacuum pump. When the vacuum pump is running, the air in the tank body is extracted through the air pipeline system to achieve the suction of feces, sewage and other liquids. The XD-70 rotary vane vacuum pump is an improved advanced product with high vacuum, low noise and long service life. It is widely used in sewage extraction equipment of sanitation departments.
3.4 Four-way valve
The vacuum pump can only rotate counterclockwise (looking at the front of the car). To extract air from the tank body or input air into the tank body, a four-way valve should be used to control it. The four-way valve is connected to the tank body, vacuum pump, oil storage tank and atmosphere respectively. By operating the four-way valve handle and changing the channel position, the suction direction of the vacuum pump can be changed. When the four-way valve handle is perpendicular to the ground, the air in the tank is pumped out through the air pipe, water-gas separator, and vacuum pump to carry out the feces suction operation.
3.5 Water-gas separator
The water-gas separator is connected to the first-stage oil-gas separator in front and then connected to the tank body through the air pipe. It is equipped with an air pipe inside, and rectangular holes are opened on both sides for air to enter and exit the tank body. During the suction operation, the air in the tank body comes out from the rectangular hole, the volume suddenly expands, the flow rate decreases, and some of the heavier water molecules adhere to the wall of the device, condense into water droplets and flow to the bottom, while the lighter gas continues to flow to the vacuum pump to achieve water-gas separation. After water-gas separation, the air humidity decreases, which can reduce its harm to lubricating oil and parts.
3.6 Oil-gas separator
The air discharged from the vacuum pump has a certain pressure and a high speed, and carries a large number of oil droplets when breaking through the oil film layer. In order to reduce oil consumption and prevent pollution, an oil-gas separator is installed. The oil-gas separator is connected to the vacuum pump in front through the air pipe and to the oil storage tank in the back. There is an oil retaining pipe in the oil-gas separator. When compressed air enters, its volume suddenly expands, the flow rate decreases, and the flow direction changes, and it flows out through the porous oil retaining pipe. As the flow rate of oil and gas molecules decreases, the impact on the wall and the hole wall intensifies, and some of the heavy oil molecules adhere to the wall of the vessel, forming oil droplets after condensation, and flow into the oil storage tank along the wall and the oil return pipe. The compressed air that has been purified for the first time flows to the top of the oil storage tank.
3.7 Oil storage tank
The oil storage tank (or secondary oil-gas separator) has one end connected to the oil-gas separator and one end connected to the four-way valve. The oil storage tank has the functions of oil-gas separation and oil storage. It is equipped with an oil retaining net, and the inlet and outlet are not connected to each other. The compressed air flowing in from the oil-gas separator must pass through multiple obstacles here before it can be discharged to the four-way valve. Due to the sudden increase in the volume of the oil storage tank, the air flow rate is significantly reduced. In addition, due to obstacles such as the oil retaining net, the oil molecules in the compressed air intensify the collision, adhere to the inner wall and the net surface, and then flow to the bottom. The compressed air that has been purified again flows to the four-way valve. A straight-through cock is provided at the bottom of the oil tank to control the amount of lubricating oil supplied to the vacuum pump. There is also a liquid level pipe to observe the amount of oil stored and the oil quality. The oil level of the oil storage tank should be in the middle of the liquid level pipe or slightly lower than the middle. Excessive oil supply affects the oil-gas separation effect and increases the oil consumption. Too low oil supply affects cooling and causes the vacuum pump to heat up too quickly. The amount of oil supply is controlled by a straight-through cock. The handle is fully open when it is at right angles to the axis of the oil inlet pipe, and fully closed when it is parallel. When it is found that there is obvious oil mist at the exhaust port of the four-way valve, the oil supply should be reduced.
3.8 Balance arm
The balance arm assembly is located at the top of the rear of the tank body. It consists of a balance seat, a connecting pipe, a counterweight, a support frame, etc. It is connected to the manure suction hose in front and the siphon pipe in the back. The balance seat can operate. Due to the setting of the counterweight, it plays a balancing role, which greatly reduces the labor intensity when taking, placing and pulling the manure suction hose. There are cleaning holes on the support frame, which are usually sealed. When the manure suction hose or siphon pipe is blocked, the cleaning hole cover can be opened to clear the blockage.
3.9 Liquid level alarm device
The liquid level alarm device is installed on the top of the tank and consists of a sensor probe, an alarm and its switch, an instrument panel, etc. The sensor probe is located in the front of the tank body, 100mm away from the top, and is insulated from the tank body. The alarm and its switch are fixed on the instrument panel and installed in the cab. When working, the power is turned on. When the liquid in the tank continues to increase and the liquid level submerges the sensor probe, the liquid level alarm circuit is automatically connected, and the sounder immediately emits a bright light and sound, conveying the message “the suction amount is in place” to the driver.
